Modern dentistry recognizes that functions of the masticatory system are best achieved by conserving and protecting remaining hard and soft tissues. For some patients, the loss of even a few teeth is traumatic. There is a strong incentive to seek dental care to preserve and restore normal speech, masticatory function, and a socially acceptable appearance. Dental implants have been developed in response to these needs.
Implant-supported fixed prostheses offer several advantages: avoidance of soft-tissue and implant trauma avoidance of bone complications caused by implant mobilization during mastication optimum fit at the bone-implant interface since the bone adapts immediately after implant placement and subsequent installation of the fixed prosthetic tooth. Such implants have been known to function well under various physiological conditions—normal food intake, which helps the body and peri-implant tissues to heal faster, stimulation of blood supply and drainage: avoidance of venous stasis, normal speech and resumption of socio-professional activities, and increased patient self-confidence.
But post-type implants and the way they are positioned have drawbacks. The boring of the bone in a vertical plane is necessarily deep to accommodate the height of the implant. But the bone may not have sufficient height. Also, the implant cannot easily pass round such obstacles as sinuses, nasal fossae, nerves, because boring is almost always done vertically.
Moreover, such implants, when inserted vertically are subject to the transmission of the forces imposed on them by mastication. They work essentially on an edge and have a strong tendency to self-bore under chewing or tooth-grinding pressures. Consequently these types of known post-type implants cannot be adapted to all bony structures.
In positioning a dental implant, it is desirable to seat the implant securely into the bone. Even the slightest mobility of the implant inside the bone often leads to ultimate rejection.
Conventionally, once the implant is set into the bone, a tapped ring or screw is set onto the outside part of the implant, which is generally a threaded rod. Onto this tapped ring or screw, a dental prosthesis is fixed, usually with a cement.
With a laterally inserted dental implant, osteotomy is initiated on the buccal or lingual/palatal aspect of the jaw. (Scortecci, Mich et al., “Implants and restorative dentistry”, p. 5 (2001).) Such implants are exemplified by the T3D implant developed by Juillet (1972) and the Diskimplant® (Scortecci, 1984). The Diskimplant® requires a specific instrument for osteotomy—a cutter manufactured of titanium. The Diskimplant® combines a horizontal disk and a post. See, e.g., U.S. Pat. No. 4,789,337, which is incorporated herein by reference.
A cutting tool may be used to prepare the lateral bone incision from one cortical layer to the other. The minimally larger implant is then impacted into the bone receptor site. Close contact at the bone-implant interface encourages immediate primary retention. A wide range of base diameters and column heights allows the surgeon to make optimal use of all available bone in both horizontal and vertical dimensions.
One advantage of such approaches is that the placement of laterally inserted implants eliminates the need for reduction of thin premaxillary ridges, in contrast to conventional screw-type implants. Subsequent crestal bone loss and gingival retraction are thus less severe and often nonexistent. As a result, a better aesthetic outcome is achieved without systematic grafting.
Such disk-column implants represent a possible solution for patients with small bone volumes. The technique can also be used to salvage situations in which an implant and/or graft have failed. Stresses are concentrated primarily at the base of the disk.
However, one of the weaknesses of conventional disk-column systems, is that the column or post that lies in the center of the disk and is relatively small in diameter. Not infrequently, fracture of the implant is often the result. Such implants, inserted in a lateral direction often break under the stresses imposed during insertion or in use. One problem of conventional approaches is that the post is often too facial to the natural tooth position in the mandible and too palatal in the maxilla.
A related problem with conventional disk-column techniques is that if the hole is oversized, or if the underlying bone is soft, the implant is not fixed securely after insertion.
The prior art is also exemplified by U.S. Pat. Nos. 4,722,687 and 4,815,974.